The release factor (RF) proteins 1 and 2 are involved in codon specific bacterial peptide chain termination. The mechanism of the codon recognition and subsequent peptidyl-tRNA hydrolysis is not understood at a molecular level. We propose to use recombinant DNA techniques to identify the regions of release factor molecules involved in these reactions. This will be accomplished by determining the in vivo and in vitro behavior of mutant RF1 and RF2 molecules generated by in vitro mutagenesis of these cloned genes. We will determine the translational and transcriptional regulation of release factor genes. We propose to clone and characterize the mammalian release factor gene using the Lambdagtll expression cloning vector. These studies will elucidate the mechanism of peptide chain termination and compare E. coli and mammalian release factors for structure, regulation, and functional domains.